串联列对象,缺少零

我试图连接两列-一小时(hh)和分钟(mm)列。有些值是双零。连接小时和分钟列时,不包括小时列。任何帮助都将不胜感激。

import pandas as pd
from urllib.request import urlopen
import datetime as dt

url = "https://www.ndbc.noaa.gov/view_text_file.php?filename=42887h2014.txt.gz&dir=data/historical/stdmet/"
data_csv = urlopen(url)
df = pd.read_csv(data_csv, delim_whitespace=True, index_col=0, parse_dates=True)

#Reset Index + remove first row + rename column
df.reset_index(level=0, inplace=True)
df = df.iloc[1:]
df = df.rename(columns={'#YY': 'YY'})

df['Time'] = df[df.columns[3:5]].apply(lambda x: ':'.join(x.dropna().astype(int).astype(str)),axis=1)

结果:

Out[203]: 
1          0:0
2         0:20
3         0:40
4          1:0
5         1:20

应该是:

Out[203]: 
1         00:00
2         00:20
3         00:40
4         01:00
5         01:20